In the conventional manufacture of semiconductor elements, for transferring a necessary pattern onto a Si substrate by the photolithography technique, a lamp light source (wavelength: 365 nm) or an excimer laser light source (KrF (wavelength: 248 nm), ArF (wavelength: 193 nm)) has been used as a light source. In more highly integrated semiconductor elements of recent years, there is an accelerating trend in microsizing a necessary pattern transfer onto a Si substrate. It is especially urgently needed to establish a new photolithography technique capable of micromachining at 100 nm or less. Consequently, a photolithography technique using an F2 laser light (wavelength: 157 nm), which is an excimer laser light with a shorter wavelength region, is now being developed.
However, because a substantial limit for resolution is typically a half size of the wavelength of the exposure light, it is assumed that machining at approximately 70 nm is the limit even if the F2 laser light is used. Therefore, it is desired that a photolithography technique using the EUV light (wavelength: 13.5 nm), which has a wavelength shorter than that of the F2 laser light by as many as one or more orders of magnitude as its light source, be developed.
In an EUV lithography technique using the EUV light, exposure by a reflection optical system is used. This is because a substance in the wavelength region of the EUV light has a refractive index of slightly less than 1, which prevents use of a refractive optical system as is used for conventional exposure light sources. Furthermore, whereas a transmission photomask is used for a conventional pattern transfer, a reflection type photomask is used in the wavelength region of the EUV light because most of the substances have high light absorbance.
As a reflection type photomask for use in such an EUV lithography method, there is proposed one which uses a reflection type photomask blank made of: a multilayer reflection film formed on a substrate, capable of reflecting EUV light; and an absorber layer formed on the multilayer reflection film and formed of a material with high absorbance of the EUV light (for example, Patent Document 1). To be more specific, the multilayer reflection film has a configuration in which two or more types of material layers whose refractive indices for the EUV light are significantly different from each other are cyclically laminated. Furthermore, the absorber layer is a lamination of layers including a tantalum nitride and layers including a tantalum. After the absorber layer is etched into a predetermined pattern, the EUV light is reflected on the multilayer reflection film with the predetermined pattern, enabling a pattern transfer onto the Si substrate. Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2001-237174.